a. Field of the Invention:
The present invention relates to a telephoto lens system and, more particularly, to a telephoto lens system arranged to obtain a telephoto ratio of 0.83 or less without using special material such as fluorite.
B. Description of the Prior Art:
For telephoto lens systems, it is generally desirable that the distance from the first lens surface of the lens system to the focal plane is short. That is, when the telephoto ratio, which is the ratio of the distance from the first lens surface to the focal plane and the focal length of the lens system as a whole, is smaller, it is more desirable as the lens system as a whole can be made more compact and it is more convenient for operation. To make said telephoto ratio small for the above-mentioned purpose, it is preferable to make the positive power of the front lens group large and to make the negative power of the rear lens group also large. For such lens system, however, distribution of power becomes unbalanced and, consequently, it becomes difficult to correct aberrations favourably. Therefore, the requirement to make the telephoto ratio small and the requirement to favourably correct aberrations are contradictory to each other. As a means to meet both of such requirements, which are contradictory to each other, some of known telephoto lens system employ a lens for which special material such as fluorite is used. In practice, however, it is not desirable to use such special material.